There are over 1.6 million apps on the Google Play Store, which makes it the largest collection of mobile apps on the planet. However, a large portion of this total is occupied by apps with overlapping functions—think social media, news, weather, music players, and various other categories where developers compete against one another to garner the largest user base.

Here at Gadget Hacks, we all have our favorite "category" apps like these, but what really gets us going is when we come across an app that does something truly unique. We've covered quite a few of these uncommon wares over the last year, so today, we'll be shining a well-deserved light on 20 apps we've found that stand alone for the functionality they offer.

1. KinScreen

If you've ever been jealous of the Samsung-exclusive feature that reads your eyes to make sure that the screen never turns off while you're actively using your phone, KinScreen offers a great alternative that should work with almost any phone. Instead of tracking your eyes, this app monitors sensors in your device to detect even the most subtle movements, ensuring that your screen doesn't turn off while you're holding your phone. More info here.

2. CaastMe

There are several apps that let you send links between your various devices, but these are generally platform-specific and require you to install software on all of your gadgets. CaastMe, on the other hand, uses QR technology to send the links, meaning you can share webpages from your Android device to any computer by just installing a single app. More info here.

3. TextStats

In today's society, the text message is one of our main forms of communication. This is a relatively recent trend in the grand scheme of things, which ultimately means that our language could be evolving at a pace we've never seen before. If you'd like to learn more about how the text message is affecting your own lexicon, give TextStats a try. This unique app will diagnose all of your sent and received messages, then show you the most commonly used words in beautiful charts and graphs. More info here.

4. Slipstream Music

Everybody has their own unique music tastes, so it's virtually impossible to make the entire party happy with a playlist drawing from one person's library. Instead of arguing over what song to play next, install Slipstream Music on each device, then everyone can contribute to the playlist by sharing their Android music library in a few simple taps. More info here.

5. Easy Copy

For the most part, when you copy text on your Android device, it's because you intend on pasting it into a different app. Rather than switching between apps to get the job done, you can use Easy Copy to send the copied text directly to the app or function that you're ultimately copying it for. More info here.

6. Google Handwriting Input

Way before we learned to use a keyboard proficiently, we were taught how to write with a pen and paper. For a lot of folks, this means handwriting will always be a more efficient method than the alternatives. Google Handwriting Input capitalizes on this concept by replacing your hunt-and-peck keyboard with a blank space that allows you to "type" with your own handwriting. More info here.

7. SMSmart

Because of the way cellular networks were launched, we get SMS and voice coverage almost everywhere, while mobile data coverage has far more dead zones. If you ever find yourself in an area without mobile internet coverage, SMSmart can potentially be a lifesaver. The app uses your near-ubiquitous SMS connection to transfer data, which means you can now use common internet services almost anywhere on the planet. More info here.

8. Backup Memory

If you have a family member who suffers from Alzheimer's disease, it's a horrible realization to think that, one day, your loved one may not recognize your face. Research has shown that constant mental stimulation can help stave off this effect, so a team of Alzheimer's analysts got with Samsung to create Backup Memory, which provides gentle reminders of your shared memories whenever you and your loved one are near each other. More info here.

9. A-BOT

If you're ever bored, lonely, or just want to chat, A-BOT has a virtual friend waiting for you 24/7. Once you've installed this chat app, you can choose from one of three bots who are programmed to answer your questions and provide witty or non-sequitur banter any time you need it. More info here.

10. AudioPocket

Many folks use YouTube as their primary source of streaming music, but the tunes comes to a grinding halt as soon as you open any other app. While there have been root workarounds for this issue, AudioPocket allows non-rooted users to play YouTube music in the background with a unique and simple share intent mechanism. More info here.

11. AppChat

With AppChat, tech support has finally been crowd-sourced. Upon opening the app, you'll see a list of all of the other apps you have installed on your phone. Simply select any app you're having issues with, then you'll be greeted by a chat room of users who also have that app installed. More info here.

12. News Dictionary

While browsing the internet or reading our favorite news feeds, we sometimes come across words we've never seen before. Rather than copying the word, then switching over to your Google app to search it in an online dictionary, an app called News Dictionary will let you get straight to the point. Simply highlight an unknown word, then press the copy button, and you'll instantly see the definition in a little pop-up window. More info here.

13. Glimpse Notifications

For most devices, when you get a new message or notification, your phone beeps and a tiny LED light starts blinking. This lets you know that a message has come in, but it doesn't give you any information about what the message is. With Glimpse Notifications installed on the other hand, your screen will wake for a brief moment when you get a new notification, allowing you to see the message sender and some of its contents before deciding if it's worth dealing with right now. More info here.

14. Microsoft Hyperlapse

The tech giant behind Windows has created groundbreaking new software that will render time-lapse videos as silky and smooth as though they were taken with a professional steadycam. Microsoft Hyperlapse, as it's called, is now available for Android devices, so we can finally take pro quality time-lapse videos with our handheld devices. More info here.

15. Wake on Gesture

How many times a day do you pick your phone up off your desk in order to check the time or see if you've got any new notifications? If you're like me, the answer is constantly. To make this habit a bit more simple (and downright cool), try Wake On Gesture, which lets you turn your display on and back off by simply waving your hand over your device. More info here.

16. Ported PS4 Remote Play

Sony has an app for their Xperia smartphones that lets you stream your favorite PlayStation 4 games over to your handheld device. Normally, this is exclusive to Sony's own devices, but developer Twisted89 has ported this PS4 Remote Play app to work with any Android device. Once you've got the app installed, you can even tweak some settings which will allow you to play your favorite games from anywhere in the world. More info here.

17. Notify Beta

Android's notifications have been revamped several times over the years, but Notify Beta will take them to a whole different level. Once you've got it set it up, all of your notifications will be colored to match the icon of their originating app, so it's a unique way to add a bit of personal flair to your device. More info here.

18. Vysor

If you leave your phone plugged into your computer at your desk, a Chrome app called Vysor can literally give you a window into your Android device. As long as you've got ADB set up on your computer, you can simply launch Vysor at any time to completely control your phone from a window on your desktop. More info here.

19. Instant Heart Rate

Many Samsung phones come with a built-in heart rate sensor, but essentially, all this is doing is shining a light through your finger, then recording the light that reflects back to get your heart rate reading. This same hardware functionality can be accomplished using the camera and LED flash on the back of any phone, and an app called Instant Heart Rate does this extremely well. After some testing, I found that this app gives readings that rival the purpose-built heart rate sensor in the Galaxy S6 in terms of accuracy, so it's a great way to measure your heart rate on a phone that doesn't have an actual heart rate sensor. More info here.

20. FiveWallpapers

Wouldn't it be nice if each of your home screen pages had a unique wallpaper? With an app called FiveWallpapers, this can easily be a reality. After choosing a wallpaper for each of your home screens, you'll get a fresh and personalized look every time you swipe over to a different page on your launcher. More info here.

Which of these unique apps did you install? Do you know of any apps offering unique functionality that we didn't cover here? Let us know in the comment section below, or drop us a line on Android Hacks' Facebook or Twitter, or Gadget Hacks' Facebook, Google+, or Twitter.

Found one that was just removed from the Play Store, and have updated the link with an APK. Can't find any others that are no longer in the Play Store. Which ones are you referring to? Could be geo-restrictions on them, which might be why you can't see them.

Cardiograph is not accurate enough to pick up SVT readings. I have not tried Instant Heart Rate during an episode, but I know RunTastics's Heart Rate is accurate. I got a reading of 238 and thought it was wrong, tested with Cardiograph at 107. I went to the ER where they registered my heart rate at 235.

I don't know how it would perform in an SVT episode, but I found Instant Heart Rate to be quite accurate when compared against the actual heart rate sensor in my Galaxy S6. Runtastic was a close second in terms of consistently getting a similar reading to the purpose-built heart rate sensor, but I definitely agree that Cardiograph was the least accurate of the bunch.